Party leader wants to spectate - How to disable?

If you're in a party and the leader starts watching a game, you get this pop-up asking if you want to join. And quite frankly, it's getting on my nerves.
I'd be content with ignoring it, but it turns out it also blocks other, more important prompts such as the new ready check. I want to disable it, but I can't find any option that lets me do so.

Can you even get rid of it? Console perhaps? There should really be a checkbox somewhere.